Expectation for Quality
High quality HDTV can be broadcasted using the 6 MHz channel-slot of one analog NTSC channel, but with over 9 times its resolution quality. The NTSC image is made of 480ix450 viewable picture elements per video frame composed of two interlaced fields and delivered at a rate of 60 fields (30 frames) per second.
Most HD broadcast compressed with MPEG-2 is transmitted as interlaced 1080i with 2 million+ pixels per video frame (1080x1920 pixels), each frame is composed of two interlaced 540-line fields delivered at the rate of 60 fields per second (30 frames).
Some HD broadcasts use the other HD 720p progressive format which has about 1 million viewable pixels per video frame (720x1280 pixels), delivered as 60 frames per second using MPEG-2 digital compression.
Although the 720p progressive HD frame has only half of the spatial pixel resolution of the 1080i frame the format’s higher frame speed makes it better suitable for sports than any interlaced format, which is prone to artifacts that result from interleaving fields of fast moving content.
Potential Quality Concerns
Digital compression (MPEG-2 for DTV) allows for a digital signal to fit into a smaller space for recording or transmission purposes. The saved space could be used for other sub-channels or services.
Digital compression can be applied in a way that was not possible with analog NTSC, and improved algorithms could make it more efficient so more content can be transmitted using the same bandwidth. However, the flexibility provides an opportunity for exploiting a quantity model rather than pursuing HD quality, which affects the supply and demand of HD content distribution.
Cable/satellite/Telco companies are known to apply over-compression and bit starving techniques to maximize their limited bandwidth so they can offer a greater number of HD channels to remain competitive.
Subscribers using small screens and/or viewing from far away may not notice image degradation as opposed to consumers that are increasingly upgrading to larger and higher resolution screens to been able to sit closer to the screen and increase the angle the view beyond THX standards and stimulate the peripheral vision to be better immersed in a movie.
Selected Output Control
Since 2002 the Federal Communications Commission (FCC) has prohibited the use of selected output controls (SOC) designed to restrict or down-res the quality of an HD signal when using the analog outputs of tuning devices (but not affecting the digital outputs, such as DVI or HDMI, because they are protected with High Definition Content Protection (HDCP).
The Motion Picture Association of America (MPAA) returned to the FCC in May 2008 for a waiver to permit SOC for a new model of HD content distribution for VoD (Video-on-Demand) HD movies just after their theater release and before they become available in Blu-ray.
The waiver was justified over the concern of the possibility that the content could be copied and distributed illegally thru piracy, and therefore negatively affect the subsequent packaged media business (DVD and Blu-ray sales) and PPV (Pay-Per-View), but it was giving the MPAA too much leeway in its implementation of SOC, affecting many consumers with non-compliant HDTVs which could be left in the dark.
SOC counts on HDMI working well and too much trust is put on the assumption that protected digital connections were implemented properly on consumer electronics, which is not the case. As of January 2009 the approval for the waiver has not been granted.
Although movie studios did not implement it yet, Blu-ray disc content is protected with a feature to reduce HD 1080i/p quality to SD when using the analog outputs of the player.
In a similar effort, in February 13, 2004, DirecTV requested the FCC to allow 'down-res' of certain non-broadcast programs over the component analog connections of their HD-STBs, anticipating that some movie studios will not make available to them some of the more popular movies if using unprotected analog outputs.
Similarly, in November 2003, to limit the indiscriminate redistribution of digital broadcast content, the FCC approved the 'Broadcast Flag' anti-piracy order; a digital code embedded into a digital broadcasting stream that would signal DTV reception equipment to activate the redistribution limit. The order was to take effect in July 1, 2005 but the court ruled that the FCC had over-stepped its authority.
In summary, artificial degradation to protect HD content has been pursued and requested several times, and its implementation affects consumers and the HD content distribution market.
Multi-casting Standard Definition Sub-channels
The 6 MHz broadcast channel slot used by 1 channel in the analog system has enough capacity to simultaneously broadcast 4-6 DTV standard definition (SD) sub-channels to meet the requirements of certain demographic areas, ethnic channels, weather, children, etc., and also multiply the advertising revenue of broadcasters.
In the analog world, those 4-6 sub-channels would have required 6MHz each and may not have existed due to TV spectrum limitations. A single HD channel typically requires the entire 6 MHz bandwidth for itself at a 19.4 Mbps bit rate to deliver a quality image using MPEG-2 compression.
Many TV stations in the US, such as PBS, are implementing a combination of HD and SD channels sharing the same 6MHz bandwidth. Based on my experience since 1998, when the bit rate of the HD sub-channel is considerably reduced by multi-casting parallel SD sub-channels the quality of the HD sub-channel deteriorates beyond acceptance, especially when fast content is viewed on large screens.
DTV Mobile and Handheld Devices
In June 2007, the ATSC received proposals regarding a DTV mobile standard to be approved in 2009. Several conditions were established, which include but are not limited to, protecting legacy receivers and existing services, be compatible with the current ATSC DTV system, and operate in the same RF channel without penalizing legacy equipment.
Samsung initially proposed their A-VSB system but later supported the approved-candidate ATSC-Mobile/Handheld (M/H) standard based on the MPH (Mobile Pedestrian Handheld) mobile DTV transmission system jointly developed by LG Electronics and Harris Broadcast.
The Mobile DTV system of transmission shares the 6MHz assigned to a terrestrial DTV channel and, like other similar mobile digital transmission systems, can generate new business opportunities for broadcasters.
However, the bits needed for the digital mobile transmission are subtracted from the bandwidth needed by the HD image (about 20% or more for A-VSB) potentially degrading the HD image quality, specially if an SD sub-channel is also multi-cast in parallel (3 transmissions: HD, mobile M/H, and SD).
The Mobile DTV standard was finally approved by the ATSC on October 15, 2009.
DTV is capable of datacasting, sharing the bandwidth typically allocated to one HDTV channel. Datacasting provides broadcasters the opportunity of new business models with the implementation of DTV, not possible with traditional analog television.
The final part 3 covers HD content in pre-recorded media, and conclusions.
Posted by Rodolfo La Maestra, November 24, 2009 9:31 AM
About Rodolfo La Maestra
Rodolfo La Maestra is the Senior Technical Director of UHDTV Magazine and HDTV Magazine and participated in the HDTV vision since the late 1980's. In the late 1990's, he began tracking and reviewing HDTV consumer equipment, and authored the annual HDTV Technology Review report, tutorials, and educative articles for HDTV Magazine, DVDetc and HDTVetc magazines, Veritas et Visus Newsletter, Display Search, and served as technical consultant/editor for the "Reference Guide" and the "HDTV Glossary of Terms" for HDTVetc and HDTV Magazines. In 2004, he began recording a weekly HDTV technology program for MD Cable television, which by 2006 reached the rating of second most viewed.
Rodolfo's background encompasses Electronic Engineering, Computer Science, and Audio and Video Electronics, with over 4,700 hours of professional training, a BS in Computer and Information Systems, and thirty+ professional and post-graduate certifications, some from MIT, American, and George Washington Universities. Rodolfo was also Computer Science professor in five institutions between 1966-1973 in Argentina, regarding IBM, Burroughs, and Honeywell mainframe computers. After 38 years of computer systems career, Rodolfo retired in 2003 as Chief of Systems Development from the Inter-American Development Bank directing sixty+ software-development computer professionals, supporting member countries in north/central/south America.